Tamarack Recharge Project

How field data collection and

modeling were used to

determine stream impacts for

the water court case

What Makes the Tamarack Model Unique?

• Nothing new in the science. Standard

MODFLOW finite difference model.

• What is unique is the large amount of data

available for the model setup and calibration.

• The litigation process may be of some interest.

Note: one novel aspect is that we used metric units

– see the slide on lessons learned

TEAM PROJECT

• Colorado State University

• CO State Engineer’s Office

• Colorado Parks & Wildlife

• Northern CO Water Conservancy District

Main Modeling Team:

Model Objectives

1. Determine timing, amount

and location of impacts to the

South Platte River.

2. Optimize the design and

operation of the recharge

project

3. Define the impacts of the

recharge operation on

wildlife habitat at the

Tamarack SWA,

Modeling Time Line (Looking Back)

Phase 1: Pilot Model (2001-2002)

Phase 2: Expanded Model and Calculated

Initial Stream Depletions for Water Court

Case (2003)

Phase 3: Water Court Negotiations -

Expanded model again and conducted

additional testing per negotiations with

Objectors (2004 – 2012).

River Starts as Constant Head Boundary

Phase 1: Focus on Main Recharge Area

Geologic Study Area:

Tamarack SWA Boundary

Based on data from 88 well logs:

• 10 Cross-sections were drafted

• 3 Contour maps were created

A

A’

B’

B

Clay, Shale, Brule

Aquitard

South Platte

River

South Platte Alluvium

Sand Dunes

North A

South A’

Schematic Cross-Section A-A’

West End of Tamarack SWA

Brule, Clay,

Shale Aquiclude

Paleo

Channel

South Platte

River

South Platte Alluvium

Sand Dunes

North

B

South

B’

Schematic Cross-Section B-B’

East End of Tamarack SWA

Brule, Clay,

Shale Aquiclude

ET and Recharge:

•Area divided into 3 zones: riparian, meadow and sand hills

•Riparian & Meadow Zones: 85% of the precipitation goes

directly to meet ET. ETS package used varies ET with depth.

•5% of precipitation recharges Sand Hills Area

Phase 1: Calibration Data

•31 groundwater and 2 stream stage monitoring locations

with survey elevation accuracy of 0.1 foot.

•10 Monitoring periods from Nov 2000 thru Oct 2001

•Total of 267 Groundwater Level Calibration Points

Phase 1: Final Calibration after PEST

Optimized K

River Floodplain=360 ft/day

Paleo Channel = 230 ft/day

Sand Hills = 360 ft/day

Optimized Sy

River Floodplain=0.2

Paleo Channel = 0.1

Sand Hills = 0.1

Phase 1: Lessons Learned

• Noticed that with high conductivities, the impact of the

recharge operations spread out considerable distances. Need

to move boundaries out in Phase II

• Good calibration, lots of data, constant head boundary

appeared reasonable.

• For a good water balance one needed to set the closure

criteria very low (0.00005 feet) for calculating stream

impacts using MODFLOW. Use of a large matrix solver

(SAMG) was also very useful

Phase 2: Expand Model and Calculate Stream Depletions

Crook Bridge

Red Lion Bridge

Expanded Time Period:

•Feb 1997 to Oct 2004

•Total Calibration Points increased to 466

Expanded Grid: both to the west and to the east

New Grid:13 by 2.5 miles

Phase 2 Calibration

Even better, Normalized RMS

1.95% with same aquifer parameters

as Phase 1

Phase 2: Calculate Stream Depletions

Methodology:

• Change ET – Allowing ET to change with depth results in

seasonal variations in stream depletions. Handled by

changing ET to negative recharge based on water budget

analysis.

• Developed scaled down model to calculate unit response

functions of all wells and ponds

• SDF – Why don’t they match model results for the ponds?

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

Ap

r-01

Ap

r-02

Ap

r-03

Apr-0

4

Mar-0

5

Ma

r-06

Ma

r-07

Ma

r-08

Ma

r-09

Ma

r-10

Cu

mu

lati

ve

Pro

jec

t R

ec

ha

rge

to

Riv

er

(ac

re-f

ee

t)

Day

Comparison of Modflow and SDF Image Well Methods Example Tamarack Recharge Project Pond

Tamarack Recharge Model (MODFLOW)

Image-Well Adjusted SDF = 65 days (Calibrated)

SDF = 65 days

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

6000

7000

Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06

acre

-feet

Date

Cumulative Project

Accretions

Cumulative TOTAL

Project Impacts

The Bigger Picture on Project Accretions

Phase 2: Lessons Learned

• Good calibration, based on lots of data, constant head

boundary appeared reasonable. Ready for Court!!

• For Tamarack, move wells as close to the river as

practical and have ponds at several locations to

provide flexibility with recharge.

• SDF method not appropriate for structures near the

edge of the aquifer.

PHASE 3 : Water Court

Unique Historical Context:

• South Platte Water Court Arena in the 2000’s was extremely

active. A large number of recharge and augmentation water court

applications submitted and trial schedule booked for many years

out.

Empire Lodge Decision (2001) – Marked the end of SEO

approval of SSPs w/o a pending water court augmentation

plan.

GASP a non-profit well-augmentation company founded in

1972 ceased operations in 2003. At its peak GASP served

~4,000 wells in NE Colorado.

• CPW: State Government Agency

PHASE 3 : Water Court

First model issue:

ET – Objectors noted that recharge raises water

levels increases ET.

Solution – Ran model with ET changing with

depth under several different operational

scenarios and determined that ET credits were reduced by ~5%. Agreement was made that

all project accretions would be decreased by

5% at the river to account for ET.

Second and Most Contentious Model Issue:

Streambed Conductivity – Objectors did not like

the S. Platte River constant head boundary for

wells close to the river.

Proposed Solution – • Expand the model across the river and change the South

Platte River boundary to a river boundary. But.. what to

use for the streambed parameters?

• Ran not 1 but 2 of the most excellent aquifer pumping

tests ever seen on the S. Platte. With such a

collaborative effort between all interested

consultant/engineers – How could it not provide the

definitive streambed conductivity value.

• Site 1: Iliff Site: 8

miles upstream from

Tamarack near the

town of Iliff. Pumping

Well 80 feet from

river, pumped for 2

days

Site 2: Red Lion Site:

– Just downstream of

Tamarack SWA.

Pumping well 120

feet from river,

pumped for 4 days

Photo courtesy of TZA

Water Engineers, Inc.

• Groundwater elevations:

Measured at 10 to 6 locations

• Stream stage: Measured at 3

stream stage sites.

Photo courtesy of TZA

Water Engineers, Inc.

Photo courtesy of Miller Groundwater

Engineering, LLC

Stream flow: Measured before, during and after pumping.

DWR hydrographers also conducted measurements for

QA/QC.

Photo courtesy of Miller Groundwater

Engineering, LLC

Aquifer Performance Test Results

1. Streambed leakance (Ksb/m) interpreted from the APT testing

ranged from: 1.69 to 775 ft/day/ft (Note that one objector

proposed a preferred value of 0.011 ft/day/ft)

2. However, only Ksb/m values below 10-20 ft/day/ft

significantly impact the Recharge Project.

3. Data from these tests was used in numerous water court case

negotiations on the Lower South Platte River.

4. Recently published journal articles indicate that the streambed

leakance parameter is grid dependant and may be best

estimated by calibration.

Decreed Results

Compromise reached a week before trial:

For wells located less than 900 feet from the river: URFs

calculated using a stream leakance value of 20

ft/day/ft for project accounting . Additional

limitations applied for leasing of any project credits.

For structures located more than 900 feet from the river:

URFs calculated using the original model with the

South Platte River modeled as a constant head

boundary.

Phase 3 - Lessons Learned:

• Model was helpful in running scenarios and analyzing

project impacts of objector proposals.

• Think twice about having more than one model objective

when going to water court.

• More stream flow calibration data would have been very

helpful!!!!

• NEVER USE METRIC UNITS – especially when going

to water court!!!

One Final Question for Discussion:

Tamarack Recharge Project negotiations

took place under “ye olde” Water Court

Rules.

Would the results or process be any

different under the 2009 Water Court

Rule 11 on Expert Testimony??????

QUESTIONS